End point control of upper extremity orthotic brace using head orientation

ABSTRACT

An end-point control of an upper-extremity orthotic brace employing head orientation is disclosed herein which is particularly well suited for quadriplegics who are able to spend some portion of their day in a wheel chair. A first gimbal is detachably secured to the patient&#39;&#39;s head by means of a head strap or the like and is interconnected by a shaft to a second gimbal which is secured to the wheel chair. The first and second gimbals have responsive means thereon such as single turn potentiometers which are responsive to azimuth, elevational and range movements of the patient&#39;&#39;s head. A control system is connected to the potentiometers for driving a powered device such as an arm brace so that the patient can control the operation of the arm brace through coordinated head movements.

Friedman Nov. 6, 1973 END POINT CONTROL OF UPPER EXTREMITY ORTHOTICBRACE USING HEAD ORIENTATION Inventor: Jon H. Friedman, Mundelein, Ill.

Iowa State University, Research Foundation, Ames, Iowa Filed: May 2,1972 Appl. No.: 249,654

Assignee:

References Cited UNITED STATES PATENTS 9 1959 Mittell et al. 3 1.1 41972 OTHER PUBLICATIONS Electrically Powered Orthotic Systems by VernonL. Y

Nickel et al., The Journal of Bone & Joint'Surgery, Vol.

Ross 3/l2.8 X

51-A, No. 2, March 1969, pages 343-351.

Primary ExaminerRichard A. Gaudet Assistant ExaminerRonald L. FrinksAtt0rney-Zarley et al.

[57] ABSTRACT An end-point control of an upper-extremity orthotic braceemploying head orientation is disclosed herein which is particularlywell suited for quadriplegics who are able to spend some portion oftheir day in a wheel chair. A first gimbal is detachably secured to thepatients head by means of a head strap or the like and is interconnectedby a shaft to a second gimbal which is secured to the wheel chair. Thefirst and second gimbals have responsive means thereon such as singleturn potentiometers which are responsive to azimuth, elevational andrange movements of the patients head. A control system is connected tothe potentiometers for driving a powered device such as an arm brace sothat the patient can control the Operation of the arm brace throughcoordinated head movements.

10 Claims, 11 Drawing Figures END POINT CONTROL OF UPPER EXTREMITYORTHOTIC BRACE USING HEAD ORIENTATION In recent years an increasingnumber of people are surviving accidents or neuromuscular diseases withextensive paralysis. Typically such disability occurs in persons whohave suffered poliomyelitis, muscular dystrophy, cerebral palsy, orlesions in the fourth or fifth cervical spinal cord region. Even thoughmodern medicine is conquering polio through vaccination, there are anincreasing number of paralysis victims resulting from automobileaccidents and hostilities such as Viet nam.

Quadriplegics, those experiencing paralysis of all four limbs, arenormally bedridden, but may spend some portion of their day wheel chairbound. Generally, such patients while lacking function in theirupperextremities do retain normal muscular control from their shouldersupward including, in some cases, the ability to raise and lowerthe'shoulder girdle.

The problem of restoring limited function by means of externalmechanical devices, termed upperextremity orthotics, is complex for anysuch mechanism must be built to follow the anatomical joints and supportthe flail extremity along with performing nearly normal upper-extremitymotion. The control of such an orthotic device is particularly difficultfor severely handicapped patients requiring multi-degree of freedomassistive braces and possessing few functional residuals for controlsignal sources.

The rehabilitation of upper-extremity function through orthotic devicesis doubly challenging for any solution must be both technologicallysound and psychologically acceptable to the patient. Realistically, onemust accept the fact that a mechanical device will never satisfactorily.substitute for a normally functioning limb. However, the objective ofthe rehabilitation of a patient is not to enable him to perform tasksmore efficiently than could be done by an attendant, but is to providesome degree of functional independence and associated personalsatisfaction. Itis of psychological advantage to allow the patientcontinuous voluntary control over the system rather than merelyinitiating a fully automated sequence even though itsperformance mightbe superior. From a purelymechanical standpoint, it would be much easierto design a manipulator which would execute a programmed routine, but itis generally agreed that mobilizing an existing arm and activelyinvolving the quadriplegic in the control system are beneficial inminimizing the feeling of being a mechanical man and encouraging anypossible increase in residual limb function.

During the past decade researchers have developed numerousupper-extremity orthotics to provide partial return of arm function toseverely paralyzed patients. Although designers have shown awareness ofcontrol and feedback, their primary attentions have been directed towardthe powering and fitting of assistive devices. Present state of the artis such that the necessary hardware can be built; but there are seriousproblems involved in designing effective control systems. At the presenttime such control systems are in a rudimentary stage.

Investigations have been conducted in many areas including studiesregarding brace configuration, actuator types, modes of control,and-suitability of various control sites. It appears that .the onlycomplete agreement among researchers concerning these topics is thatthere is general disagreement regarding the correct approach to theproblem.

Arm function is extremely complex; in fact, there are eleven degrees offreedom in the arm not including the hand. The trend in the developmentof orthotic brace configurations has been to increase the number ofdegrees of freedom in the hope of providing a more flexible andfunctional brace. One of the latest devices, the Rancho Electric Arm,has 7 of freedom which is thought by some investigators to be theminimum number required to restore reasonable arm movement. These sevenjoints include two joints at the shoulder, two at the elbow (oneflexion/extension and the other humeral rotation), forearm rotation,wrist flexion and hand prehension. However, generally associated with anincrease in the number of degrees of freedom is an undesirable increasein the bulk of the brace and complication of the control system.

-*-The 'decisionregarding whether to use pneumatic or electricalactuators to operate an orthotic brace is not clear-cut even thoughseveral studies have been conducted in this area. However, both types ofactuators have been used successfully and their performance iscomparable. The most widely used external-power source has been CO gasin the pneumatic systems. The actuators for these systems are pistonsand McKibben artificial muscles. More recently electrical systems havebeen used with permanent magnet 24 volt DC. motors as actuators.

Studies in the past have concentrated on two basic approaches: first, tooperate an orthotic brace completely by direct patient control, andsecond, to make such control fully automatic. In direct control schemes,the patient excercises continuous control over the motion of theassistive device. Automatic control, once initiated allows a movement toprogress to its completion without further conscious attention.There-are obvious problems with both methods.

Direct patient control is difficult because of the number of degrees offreedom which must be controlled. Devices in this category presentlyrequire separate sites or switches to control each joint of the brace.The disadvantages of this type of system are that coordinated motion ofthe brace is difficult since multiple sites must be activatedsimultaneously and smooth positioning of the brace is relatively'unobtainable with an on-off control system. The results of one studyindicate that a polio patient required motions to take five bites offood and 45 motions to pick up a cup and drink from it using the directtype of control. In general, presently developed systems require adegree of mental attention that is excessive, particularly in terms ofthe frequently unnatural motion that results.

On the other side of the spectrum is the completely automatic device inwhich the patient simply selects which one of several programmed motionswill be performed. There are several problems associated with thisapproach including reduced adaptability due to a limited number ofmovement sequences, the expense of peripheral equipment normallyassociated with such a system, and substantially reduced patientparticipation.

In recent years, one of the most active areas of interest has been indiscovering anatomical sites which are suitable for generating controlsignals. Many exotic control sources have been proposed for severelyparalyzed patients having limited effector sites. In general, higherorder quadriplegics have only the following control sites available:relative motions-of body parts above the shoulders, electromy ographicsignals (EMG), electroneurographic signals (ENG),electroencephalographic signals (EEG), and sound or speech.

Investigators have considered several schemes for transforming relativemotion of parts of the body into usable signals. Included among thesestudies have been attempts to use head motion to actuate simple arraysof switches, a light source attached to eyeglasses that may be directedto activate appropriate photocells, and switches activated by eyebrowmotion. One of the most commonly used techniques has been the operationof a switch or strain gauge array by means of the tongue. One of thelatest approaches has been an attempt to use eyeball motion as thesignal source. This method utilizes the fact that light shining on theeye is reflected back toward the source in varying amounts depending onthe eye orientation. Eye motion will eventually be used to generatesignals for azimuth and elevation inputs to a coordinate converter.Preliminary findings indicate that drift, blinks, and light intensitieswill be a major source of problems.

Electromyographic signals, the electrical activity associated withmuscle activity, have been used in various control schemes. The mainproblem with such systems has been the excessive amount of effortrequired to activate multiple sites in comparison to the minimalfunction provided. Electroneurographic signals, the potential activityfrom the nerves, and electroencephalographic signals, the potentialactivity of the central nervous sytem, have been proposed as signalsources, but present techniques and signal pattern recognition problemsmake them impractical. The use of sound or speech to activate electricalcircuits by using acoustical filters appears feasible, but again thecontrol of several actuators by this method would be difficult and itsoperation would limit communication of the patient during braceoperation.

The state of the art is such that systems presently developed or beingdeveloped provide limited restoration of upper-extremity function, buteither require extreme effort to generate coordinated motion or totallylack active patient participation.

Therefore, it is a principal object of this invention to provide anend-point control of an upperextremity orthotic brace using headorientation. 7

A further object of this invention is to provide a means for controllinga powered device entation.

A further object of this invention is to provide a gimbal which issecured to the patients head by a head strap and which is interconnectedby a shaft to a second gimbal which is secured to the wheel chair, thegimbals and shaft permitting the reading of azimuth, elevational andrange changes in the head position.

A further object of this invention is to provide a device having twosets of gimbals to measure the actual angles of azimuth and elevation asreferenced to the wheel chair.

A further object of this invention is to provide a control system foroperating an orthotic brace through vertical, horizontal and rearwardand forward head movement.

These and other objects will be apparent to those skilled in the art.

.This invention consists in the construction, arrangements andcombination of the various parts of the deusing head orivice, wherebythe objects contemplated are attained as hereinafter more fully setforth, specifically pointed out in the claims, and illustrated in theaccompanying drawings, in which:

FIG. 1 illustrates the end-point coordinates;

FIG. 2 is a side view illustrating the end-point control of anupper-extremity orthotic brace;

FIG. 3 is a top view of the gimbal arrangement;

FIG. 4 is a front view of the fixed gimbal;

FIG. 5 -is a front view of the head mounted gimbal;

FIG. 6 schematically illustrates the manner in which the elevation angleis measured;

FIG. 7'schematically illustrates the-brace axes;

FIG. 8 is a schematic illustration of the control system;

FIG. 9 is a schematic illustration of the electrical circuitry of theweighting circuit and comparator;

FIG. 10 is a schematic illustration of the electrical circuitry of thepulse width modulating circuit; and

FIG. 11 is a schematic view of the electrical circuitry of the motordrive circuit.

Based on the limitations of existing upper-extremity orthotic systems,the design of an improved assistive device requires the selection of amore suitable control site. The desire to initiate movement of anorthotic device originates at some conscious level in the centralnervous system and takes the form of some voluntary physical action.Head orientationis particularly suited as a control site, since the headhas its own vertical sensing element and smooth control of head motionover a wide dynamic range is possible.

Azimuth, elevation, and radius of action together generate avector-distance function that can serve to specify the end-pointcoordinates or an orthotic brace. This end-point coordinate system,shown in FIG. 1, is in the form of spherical coordinates. Positions ofthe hand that are normally traversed in routine self-care activities maybe specified in terms of this vector- .distance function. An array oftransducers was designed and constructed to provide a continuousmeasurement of the angular orientation of the head together with asimulated signal of desired range based on head position. This device isshown in FIG."2 and is generally identified by the reference numeral 10.Device 10 generally consists of two gimbals 12 and 14 interconnected bya small aluminum shaft 16 which senses movements of gimbal l2.

Gimbal 12 is strapped to the patient by an elasticized headband 18 andthe second gimbal 14 is attachd to a mounting 20 on the back of thewheel chair 22. The. device allows the patient to rotate his headapproximately 100 in the vertical, plane and degrees in the horizontalplane with negligible restraint. The only significant restriction is inthe forward-backward motion of the head which is limited toapproximately two inches of travel by the range transducer.

It is necessary to use two sets of gimbals to measure the actual anglesof azimuth and elevation as referenced to the wheel chair. As shown inFIG. 6, the true elevation angle is obtained by adding the correspondingangles of both gimbals. This same relationship holds true for measuringazimuth. Thus, the gimbal 14 mounted on the wheel chair measures thenecessary correction to account for the fact that the gimbal 12 strappedto the patient measures angles with respect to the interconnecting shaft16 rather than to a fixed set of axes.

A radius of action or desired range is simulated by the patientsrelative forward-backward positioning of his head which is convertedfrom a linear displacement of the interconnecting shaft 16 to therotation of potentiometers 24 and 24'. Minimum range is selected by thepatient moving his head to the most forward position, a somewhat naturaleating posture. Range is increased by the patient moving his headbackward.

More specifically, gimbal 12 comprises a U-shaped yoke 28 which isstrapped to the patients head. The legs 30 and 32 of yoke 28 havepotentiometers P mounted thereon respectively which are operativelyconnected to the shafts 34 and 36 extending inwardly from legs 30 and 32respectively. The inner ends of shafts 34 and 36 are rigidly secured tosides 38 and 40 of block 42. Potentiometers P, are mounted on the topand bottom portions of block 42 and are operatively connected to theshafts 44 and 46 extending from block 42. The inner ends of shafts 44and 46 are rigidly secured to support 48 which is secured to shaft 16.Thus, movement of the patients head is an upwardly direction causes yoke28 to rotate or pivot with respect to shafts 34, 36 and the block 42.Such movement of yoke 28 causes the shafts 34 and 36 to change theresistance of the potentiometers P due to their connection with theshafts 34 and 36.

Movement of the patients head in a sideway manner causes yoke 28 to inturn rotate or pivot block 42 with respect to support 48 and shafts 44,46. Such movement causes shafts 44 and 46 to change the resistance inthe potentiometers P due to the connection therewith. Forward orbackward movement of the patients head causes shaft 16 to becorrespondingly moved. The patient can simultaneously controlpotentiometers P and P by moving his head sideways and vertically.

Gimbal 14 comprises a U-shaped yoke 50 which is secured to the wheelchair. The legs 52 and 54 of yoke 50 have potentiometers P ,mountedthereon respectively which are operatively connected to the shafts 56and 58 extending inwardly from legs 52 and 54 respectively. The innerends of shafts 56 and 58 are rigidly secured to sides 60 and 62 of block64. Potentiometer P is mounted on the top of block 64 and is operativelyconnected to the shaft 66 extending from block 64. A shaft 68 alsoextends from block 64. The inner ends of shafts 66 and 68 are rigidlysecured to support 70. Shaft 16 slidably extends through support 70.Rotational movement of shaft 16 causes pivotal movement of support 70 bymeans of a keyway arrangement. Support 70 has a pair of rearwardlyextending legs 72 and 74 having the range potentiometers P mountedthereon. The shafts 76 and 78 are connected to the potentiometers P andhave a gear or roller 80 mounted thereon which engages the shaft 16 tosense any longitudinal movement of the shaft 16.

Thus, elevational movement ofthe patients head causes shaft 16 to pivotsupport 70 and block 64 with respect to yoke 50 so that the resistancein the elevation potentiometers P is changed. Sideways movement of thepatients head causes shaftl6 to pivot support 70 with respect to block64 to change the resistance in the azimuth potentiometers P Longitudinalmovement of shaft 16 (range) causes the resistance to be changed in therange potentiometers P Head orientation is well suited as a control sitebecause of the ease in measuring a set of coordinates which fullyspecify the desired end-point of an orthotic brace 26. This naturalsignal source requires minimal concentration, effort, and training toactivate. It allows a patient to directly control the trajectory of anassistive device through head motion, is cosmetically acceptable, andplaces few restrictions on patient movement. 1

The orthotic brace 26 is shown in FIG. 2 and is readily available. Thebrace 26 was originally designed as a pneumatically actuated feeder buthas been converted to electric motor drive. Electrical actuators arepreferred since there is a ready source of battery power in the electricwheel chairs.

The orthotic brace 26 allows for three powered motions; a horizontaldisplacement, a vertical displacement, and an elbow flexion/extension.The horizontal and vertical displacements are completely independentmotions and together contribute to the abduction/adduction andflexion/extension of the upper arm. A coiled spring lessens the effectsof gravity by assisting in the vertical support of the brace and thearm. A telescopic rod and tube connected to the elbow flexion/extensionunit serves as an attachment for the hand support. A molded elbow andforearm trough is attached to this unit and acts as a support for theforearm which is held secure in the trough by a Velcro strap. There areseveral sites for adjustment of the orthosis to assist in the fitting ofpatienls.

The exact power requirements of upper-extremity orthotics are difficultto define, not only because of the wide age span of patients, but alsobecause of variations in size from an atropied limb to a normal limb. Toallow for this wide range of torque requirements permanent magnet motorswith linear load-speed curves areutilized with adjustable gaih drivecircuitry. These 24 volt DC motors have planetary ger heads with a 639:1gear reduction and provide the capability of 288 oz. in. torque undercontinuous load conditions. This type of motor is particularly desirablebecause of its relative compactness and light weight. Although there issome noise associated with their opeation, it is not distracting and mayprovide some useful-function as an audible feedback.

All joints of the orthotic brace, three driven and one free, arecontinuously monitored by transducers. These small potentiometersprovide measurements of the brace angles and are mounted with couplingswhich allow easy adjustment for proper reference.

The control system was designed to be volitional, proportional, andvectorial". Volitional means the patient can start, stop, or modify thecourse of action. Proportional, control means that by varying his motionthe patient can control the rate of action or the force exerted.Finally, vectorial control means that a particular motion can beachieved in a smooth direct of a desired end-point. Most simply stated,this system allows a patient to regulate the location of his handthrough head orientation. To fulfill the requirements of end-pointcontrol it is necessary to generate control equations which fullyexpress the relationship between 7 the head oriented coordinates andthose of the orthotic brace.

FIG. 7 is a diagrammatic representation of both the brace and headoriented coordinate systems. The brace angles include: F, the motordriven brace angle in horizontal displacement; G, a motor driven braceangle in the vertical plane; and J, a motor driven angle of elbowflexion/extension. The axis of rotation for angle J is offset 40 fromthe vertical thereby giving this motion both a vertical and horizontalcomponent.

The equations expressing the relationship between the head orientedcoordinate system and the orthotic brace coordinate system, interms of adesired end point (x, y, z), are as follows:

z: RsinE d sinG d sinflcosJ K,

where,

d 7% inches d 7% inches d 18 inches The K K and K terms account for therespective x, y, and z displacements between the two sets of axes andare dependent upon the adjustment of the brace in fitting a patient.

However, theseexact equations are relatively complex trigonometricexpressions and their solution requires considerable computationalequipment or a costly series of resolver chains in place of the low costpotentiometers. At the sacrifice of some accuracy, but with considerablecost reduction, a simplified set of control equations are used. Theseequations are based on the geometry of the brace along with someconsideration for the natural motionthat is being simulated. The resultof this simplification is an algorithm of weighting factors which can beoptimized to satisfacto' rily duplicate natural arm motions and tominimize the error in the end-point positioning of the brace withrespect to head orientation.

The horizontal and vertical displacements of this assistive device arecompletely independent motions, but actuation of the elbowflexion/extension unit results in both horizontal and verticalcomponents. A straightforward way of relating the head generated signalsof azimuth, elevation, and range to the motorized angles of the brace isto assume that the elbow flexion/extension actuator is primarilyinvolved in changing the desired range of the hand. This assumption isreasonably valid in that the actuators controlling horizontal andvertical displacements by themselves have minor effects in changing theradius of action of the hand. Based upon these approximations, theactuator for horizontal displacement angle F, and. the actuator forvertical displacement, angle G, are coupled to desired range signals tocompensate for the fact that elbow flexion/extension has componentsbesides range associated with its motions. These greatly simplifiedcontrolequations are as follows:

where all K terms are experimentally determined weighting factors. Thereare two major sources of error which limit the accuracy of thisapproach. First, the horizontal and vertical components associated withelbow flexion/extension are not linear functions of angle J as assumedin the equations above. And second, motions produced'by the horizontaland vertical actuators do have components of range involved with theirdisplacements which are not reflected in the control equations. However,despite these limitations the expressions appear to be useable.

FIG. 8 is a block diagram of the overall control system for onemotorized component. Azimuth, elevation, range, and appropriate braceangles are weighted together by a resistive network and the result, acomputed angle, is compared to the actual brace angle. This isaccomplished by the differential amplifier arrangement shown in FlG. 9.The two outputs of this circuitry are directly related to the magnitudeof the error existing between the desired and the actual brace angle,but are invfersely related to each other about a 6 volt D.C. reference.The next stage of the electronics consists of a pair of pulse widthmodulating circuits, shown in FIG. 10. If an output from the comparatorstage exceeds a prescribed level, which is adjustable, the pulse widthmodulating circuit will generate a signal with a duty cycle which is afunction of the error. Both the dead zone and the gain of this circuitare adjustable thereby allowing the control sensitivity, motor speed,and dead zone to bematched to the limitations and requirements for aparticular direction and I speed of an actuator to drive the errorwithin an allowable range. Each of these circuits is mounted on anindividual printed circuit board and inserted in a rack mounted on'theback of the wheel chair. Two 12 volt -D.C. batterieaconnected in series,are used as a power useful in sensing the external load and/or thevelocity of the limb.

The system disclosed herein provides the severely paralyzed patient witha simple, low cost assistive device which can be operated with minimaleffort, concentration, and training. The key feature in this design isthe use of head orientation as the controlling signal. This natural siteof independent motion in azimuth and elevation is cosmetricallyacceptable, allows the patient to excercise direct control of theorthotic brace, and greatly simplifies the control problem by expressingall parameters in terms of the desired endpoint.

While the gimbal arrangement has been described herein as being wellsuited for controlling devices such as an orthotic brace, it should benoted that the gimbal arrangement could be used to controldevices otherthan orthotic braces. Head orientation could be used by any patientswith upper extremity handicaps to operate manipulators, typewriters,etc.

Thus it can be seen that a novel system has been provided which permitsthe severely paralyzed patient to operate a device through the use ofhead orientation. Thus it can be seen that the device accomplishes atleast all of its stated objectives.

I claim:

1. In combination,

a chair means for supporting a patient therein;

a first gimbal means for detachable connection to the patients head, asecond gimbal means secured to said chair means, interconnection meansinterconnecting said first and second gimbal means for sensing movementof said first gimbal means in response to head movement,

said first and second gimbal means having responsive means thereon whichis responsive to azimuth, elevational and range movements of thepatients head,

a powered device,

and a control system' connecting said responsive means and said powereddevice to permit the patient to control the operation of the device byhead movements.

2. The combination of claim 1 wherein said powered device is an orthoticbrace.

3. The combination of claim 2 wherein said brace is an upper extremitybrace.

4. The combination of claim 1 wherein said chair means is a poweredwheel chair, said control system being mounted on said wheel chair.

5. The combination of claim 1 wherein said interconnection meanscomprises a shaft.

6. The combination of claim 1 wherein said responsive means comprisespotentiometers which are operatively secured to said first and secondgimbal means,

7. The combination of claim 5 wherein said first gimbal means comprisesfirst and second supports which are pivotally movable with respect toeach other, said responsive means on said first gimbal meanscomprispotentiometer means being responsive to relative ing first andsecond potentiometer means connected to said first and second supportsand being responsive to relative movement of said supports.

8. The combination of claim 7 wherein said second gimbal means comprisesa third support secured to said chair means, a fourth support pivotallysecured about a horizontal axes to said third support and a fifthsupport pivotally secured about a vertical axes to said fourth support,said fifth support being secured to said shaft and being movabletherewith during the elevational and azimuth movements of the patientshead, said responsive means comprising third and fourth potentiometermeans operatively secured to said third and fourth supports, said thirdpotentiometer means being responsive to relative movements of saidfourth support with respect to said third support, said fourth movementof said fifth support with respect to said fourth support.

9. The combination of claim 8 wherein a fifth potentiometer means isoperatively secured to said shaft which is responsive to longitudinalmovements thereof.

10. In combination,

a chair means for supporting a patient therein;

a first support means for detachable connection to the patients head,

a second support means secured to said chair means,

interconnection means interconnecting said first and second supportmeans for sensing movement of said first support means in response tohead movement,

said first and second support means having responsive means thereonwhich is responsive to azimuth, elevational and range movements of thepatients head,

a powered device,

and a control system connecting said responsive means and said powereddevice to permit the patient to control the operation of the device byhead movements.

1. In combination, a chair means for supporting a patient therein; afirst gimbal means for detachable connection to the patient''s head, asecond gimbal means secured to said chair means, interconnection meansinterconnecting said first and second gimbal means for sensing movementof said first gimbal means in response to head movement, said first andsecond gimbal means having responsive means thereon which is responsiveto azimuth, elevational and range movements of the patient''s head, apowered device, and a control system connecting said responsive meansand said powered device to permit the patient to control the operationof the device by head movements.
 2. The combination of claim 1 whereinsaid powered device is an orthotic brace.
 3. The combination of claim 2wherein said brace is an upper extremity brace.
 4. The combination ofclaim 1 wherein said chair means is a powered wheel chair, said controlsystem being mounted on said wheel chair.
 5. The combination of claim 1wherein said interconnection means comprises a shaft.
 6. The combinationof claim 1 wherein said responsive means comprises potentiometers whichare operatively secured to said first and second gimbal means.
 7. Thecombination of claim 5 wherein said first gimbal means comprises firstand second supports which are pivotally movable with respect to eachother, said responsive means on said first gimbal means comprising firstand second potentiometer means connected to said first and secondsupports and being responsive to relative movement of said supports. 8.The combination of claim 7 wherein said second gimbal means comprises athird support secured to said chair means, a fourth support pivotallysecured about a horizontal axes to said third support and a fifthsupport pivotally secured about a vertical axes to said fourth support,said fifth support being secured to said shaft and being movabletherewith during the elevational and azimuth movements of the patient''shead, said responsive means comprising third and fourth potentiometermeans operatively secured to said third and fourth supports, said thirdpotentiometer means being responsive to relative movements of saidfourth support with respect to said third support, said fourthpotentiometer means being responsive to relative movement of said fifthsupport with respect to said fourth support.
 9. The combination of claim8 wherein a fifth potentiometer means is oPeratively secured to saidshaft which is responsive to longitudinal movements thereof.
 10. Incombination, a chair means for supporting a patient therein; a firstsupport means for detachable connection to the patient''s head, a secondsupport means secured to said chair means, interconnection meansinterconnecting said first and second support means for sensing movementof said first support means in response to head movement, said first andsecond support means having responsive means thereon which is responsiveto azimuth, elevational and range movements of the patient''s head, apowered device, and a control system connecting said responsive meansand said powered device to permit the patient to control the operationof the device by head movements.